Those are not SVG icons! Stippi didn't just design some of the icons, but also invented a brand new file format. And this was actually a quite important improvement! The HVIF, or Haiku Vector Icon Format, is so compact that the icon usually fits in the file's inode in the file system. This means that the icon data is right there when a directory is to be listed, without first reading the content of separately stored icon files, bringing very welcome speed improvements. Rendering HVIF is also much, much faster than rendering a general purpose vector format, especially SVG which is XML based.